Issue34

E. Marcisz et alii, Frattura ed Integrità Strutturale, 34 (2015) 379-386; DOI: 10.3221/IGF-ESIS.34.42 383 From the diagrams in Fig. 6, it can be observed that the values of stresses and strains in registered histories slightly oscillate around some fixed values. A small decrease of stress can be observed at the initial stage of test (Fig. 6a), whereas strain presents the opposite behaviour (Fig. 6b). Thereafter, both histories stabilize during the test. Fig. 7 presents 2024 aluminum alloy fatigue characteristics, determined on the base of tests with controlled energy parameter amplitude W a at bending. The tests have been performed at four levels W a = 0.2, 0.3, 0.35, 0.4 MJ/m 3 . Figure 7 : The fatigue characteristic (W a -N f ) of 2024 aluminum alloy under bending with a controlled amplitude of the energy parameter. Fig. 8 presents 2024 aluminum alloy fatigue characteristics, determined with controlled amplitude of the bending moment  a at bending. In the range of finite lifetime, the tests have been executed at five levels  a = 187.5, 200, 232, 233, 255 MPa. At least two specimens were tested at each of stress levels. Figure 8 : The fatigue characteristic (  a -N f ) of 2024 aluminum alloy with controlled amplitude of the bending moment Fig. 9 presents fatigue characteristic of 2024 aluminum alloy with controlled amplitude of the bending moment  a and energy parameter W a . Knowing the values obtained during tests at controlled amplitude of the bending moment  a =